Foamable coupling for lamp assembly and methods for using the coupling

ABSTRACT

A foamable copolymer based coupling is provided for securely affixing a light emitting glass lamp in a metal base to form a lamp assembly. The copolymer is preferably selected from ethylene vinyl acetate, ethylene methyl acrylate, and combinations thereof. The foamable coupling may be placed around one end of the glass lamp or in the lamp base before the lamp and base are matingly engaged. The assembled lamp is then heated to a temperature, which causes the foamable coupling to expand and securely affix the lamp in the base.

FIELD OF THE INVENTION

This invention relates to a foamable coupling comprising an ethylenevinyl acetate (EVA) and/or ethylene methyl acrylate (EMA) basecopolymer. In particular, this invention relates to a lamp assembly inwhich the foamable coupling securely affixes a light emitting glass lampin a metal base. This invention further relates to methods for securingglass tubes or bulbs in metal bases using the foamable coupling.

BACKGROUND OF THE INVENTION

In the manufacture of lamp assemblies, a light emitting glass lamp suchas a fluorescent glass tube or an incandescent glass bulb usuallycontaining wires or filaments is affixed to a metal end cap or base by athermosetting cement. In order to affix the glass lamp to the metalbase, the base is lined with a generous amount of cement, and is thenwarmed to soften the cement. The base is then placed on one the end ofthe glass lamp and the cement is heated and cured while the base andglass lamp are securely held together.

Typical cement formulations comprise mixtures of synthetic phenolicresins like novolak and natural resins like shellac and rosin. Thesebinders are used along with fillers, hardeners, solvents, and otherreactive components like aldehydes, ammonia, and metal hydroxides forin-situ condensation polymerization. Other cements may contain epoxides,polyesters, alkyds, acrylics, or silicone resins.

These cements, however, have several drawbacks. First, the cements haveshort shelf lives because of the need for solvents like trioxane orhexamethylenetetramine and other reactive components like aldehydes,ammonia, or metal hydroxides. Second, the use of these organic solventsin the high temperature curing process for these cements creates bothhealth risks and environmental concerns. Third, accurate application ofthese cements is difficult, and as a result, a relatively large amountof cement must be used to adhere a glass lamp to a metal base. Fourth,because it is very difficult to apply these cements evenly to lamp baseseither an insufficient amount of cement is used resulting in inadequatebonding between the glass lamp and the base, or too much cement is usedresulting in lamp breakage or impairment of the function of the lampassembly. Finally, these cements often cannot withstand the hightemperatures, which are required during the lamp assembly manufacturingprocess.

Various attempts to improve the methods for adhering glass lamps inmetal bases have been made and some of the compositions and methods forthis purpose are described in the prior art. For example, British PatentSpecification No. 1,139,266 discloses the use of an insulating foamablehollow cylinder comprising a novolak, hexamethylenetetramine, anddolomite resin to fill the free space in an electric incandescent lampbase in order to prevent arc formation between the current supplyconductors or between such conductors and the base. The hollow cylinderis placed in the base, and the incandescent lamp or bulb is then affixedto the base with a conventional thermosetting cement. During thecementing process, the hollow cylinder will foam and fill the free spacein the base and prevent formation of arcing between the current supplyconductors.

German Patent Application No. 1,958,307 discloses the use of a foamableputty to secure a gas-filled incandescent lamp to a base. The putty orcement is a conventional heat curable putty with a heat foaming additivecomprising phenolic resin, hexamethylenetetramine, marble flour, andtalc powder. The putty is spread in the upper edge of the lamp base, thelamp is placed in the base, and the base is heated so that the puttyfoams and fastens the glass lamp to the base.

Japanese Patent Application (Kokai) Nos. 56-9931 and 56-9932 disclosethe use of dimer acid based polyamide and polyacrylamide (and itscopolymer polyvinyl) based resin cements for use in securing glass tubesor bulbs to bases. While polyamide and polyacrylamide based cements maybe more environmentally friendly, they suffer from other disadvantages.These cements are quite expensive, and on prolonged exposure to heatbecome brittle due to oxidative degradation. Finally, polyamides arealso very tacky, and as a result, are difficult to compound into usablecompositions.

Japanese Patent Application (Kokai) No. 59-121764 discloses the use of afoamable tape comprising an epoxy or polyester resin and a blowing agentto secure a fluorescent tube or incandescent bulb to a metal base. Inorder to secure the glass tube or bulb to the base, the foamable tape iswound around the end of the glass bulb, the bulb is placed in a base,and the resulting assembly is heated to 120° C. to foam or expand theadhesive tape. However, it is very difficult to manufacture a tape outof epoxy or polyester thermosetting resins like these, and stillmaintain control over the tape's dimensions.

Patent Application WO 98/28359 discloses the use of an elastic foamablesealing material, which can be used in lamp housings. The foamablesealing material comprises modified silane polymers, fillers, silica,softeners, and organo-functional low-molecular weight silanes.

U.S. Pat. Nos. 4,988,912 and 4,888,519 disclose using thermoplasticresin rings comprising polyetherimide and polyethersulphone respectivelyfor adhering a lamp vessel, shown as a bulb, to a base. In use, thethermoplastic ring is heated to a temperature of 150-200° C. and placedon the end of a heated lamp vessel. The lamp vessel is then mated withthe base, and the base is heated to a temperature of 400-450° C. to meltthe ring thereby adhering the lamp vessel and base. The disclosedthermoplastic resin rings are not foamable in nature and suffer from thedisadvantage that high heat is required to sufficiently melt the ringsto secure the lamp vessel to the base.

In addition, numerous patents disclose the use of EVA based foamablematerials for various unrelated applications. For example, U.S. Pat. No.6,114,004 to Cydzik et al. and U.S. Pat. Nos. 6,107,574, 5,979,902, and5,931,434 to Chang et al., which are all owned by the assignee of thepresent application, disclose the use of sealing articles comprising adriver and a sealer in which the driver and sealer are EVA basedfoamable compositions. The sealing articles are useful in sealingcavities in automobile frame channels and substrates such as electricalconductors and optical fibers. While the foamable compositions of Changet al. and Cydzik et al. may be able to withstand elevated temperaturesfor relatively short periods of time, the foam structure in thesecompositions would collapse on prolonged exposure to elevatedtemperatures for and extended period of time, such as 140° C. for 2000hours. Also, the useful time-temperature window for installation ofthese compositions is very narrow because exposure to high temperaturesresults in grossly non-uniform cell structure. Furthermore, thesefoamable compositions would not be able to withstand exposure tocommonly encountered hot and humid storage conditions, such as 45° C. at80% relative humidity for one week.

U.S. Pat. No. 4,456,784 discloses the use of a foamable cylindricalbarrier for use in an electrical conduit to prevent the flow of vaporthrough the conduit. The disclosed foamable cylindrical barrier maycomprise an EVA copolymer and a sufficient amount of dicumyl peroxide tocause the barrier to foam.

PCT Patent Application No. WO 97/47681 discloses a reversibly deformablepressure sensitive adhesive foam comprising an EVA copolymer and anexpandable particulate material comprising a polymeric shell and avolitizable fluid or gas core. The disclosed pressure sensitive adhesivefoam is useful for decorative trim pieces on automotive bodies,appliances, home and office furnishings and equipment. The disclosedfoam would not be suitable for use in securing glass lamps to bases, asthe underlying technology and normal applications for such foams areentirely different than that of the present invention. As a result, thepressure sensitive adhesive foam is not designed for and would not becapable of withstanding prolonged exposure to elevated temperatures,i.e., 140° C. for 2000 hours, as required by IEC standards.

While the above foamable compositions and methods for securing glasslamps in bases may be suitable for their intended purpose, it isbelieved that there is demand in the industry for an improvedcomposition for securing light emitting glass lamps in bases, especiallyone that can be easily and inexpensively prepared, is environmentallyfriendly, and which can also withstand the elevated temperatures lampassemblies are required to endure for extended periods of time. It isfurther believed that there is a demand for an improved composition forsecuring light emitting glass lamps in bases which is easy to handle andcan be used in existing manufacturing process for lamp assemblies.

BRIEF SUMMARY OF THE INVENTION

The present invention provides for an improved foamable coupling used tosecurely affix a light emitting glass lamp such as a fluorescent tube orincandescent bulb in a metal base to form a lamp assembly. The couplingcomprises a base copolymer and at least one blowing agent wherein thecopolymer is selected from the group consisting of ethylene vinylacetate, ethylene methyl acrylate, and mixtures thereof. The couplingmay also comprise a chemical crosslinking agent, a radiationcrosslinking promoter, a tackifier, an antioxidant, a blowing agentactivator, or a filler, or combinations thereof. The present inventionfurther provides an improved method for securely affixing a glass lampin a base using the foamable coupling. The coupling is placed around oneend of the glass lamp or inside the base. The glass lamp is theninserted into the base, and the base is heated to a sufficienttemperature for a sufficient time to expand the coupling and securelyaffix the glass lamp in the base.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a lamp base and a side elevationalview of a portion of a fluorescent light emitting glass lamp, which forma lamp assembly;

FIG. 2 is a perspective view of a ring-shaped foamable coupling of thepresent invention;

FIG. 3 is a cross-sectional view of the ring-shaped foamable coupling ofFIG. 2 taken along line 3—3;

FIG. 4 is a top view of a C-shaped foamable coupling of the presentinvention;

FIG. 5A is a cross-sectional view of the foamable coupling of FIG. 4taken along line 5—5;

FIG. 5B is a cross-sectional view of the foamable coupling of FIG. 4taken along line 5—5 with an added adhesive layer;

FIG. 6 shows the glass lamp and metal base of FIG. 1 with across-sectional view of a ring-shaped foamable coupling placed aroundthe glass lamp;

FIG. 7 shows the glass lamp and metal base of FIG. 6 in which the glasslamp has been inserted into the base;

FIG. 8 shows a lamp assembly with the glass lamp secured in a metal baseby a coupling of the present invention, which has been foamed and cured;

FIG. 9 shows the glass lamp and metal base of FIG. 1 with an unfoamedring-shaped coupling of the present invention placed in the base;

FIG. 10 shows the glass lamp and metal base of FIG. 9 with the glasslamp inserted in the metal base;

FIG. 11 is a perspective view of the metal base of FIG. 1 with a foamedring-shaped coupling of the present invention placed inside the base;

FIG. 12 is a photograph of test disks made in accordance with thefoamable compositions of the present invention; and

FIG. 13 is a photograph of test disks made in accordance with thefoamable compositions of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the Figures, where like numerals denote like elementsof the invention, FIG. 1 is a partial cross-sectional view of agenerally cylindrically shaped lamp base 1 and a side elevational viewof one end of a cylindrically shaped glass lamp 3. The glass lamp andbase form the components of a lamp assembly. As shown in FIGS. 1 and 11,the lamp base 1 has a top 5 and a generally cylindrical sidewall 7terminating at the top 5 and at a lower rim 9. The sidewall 7 of thebase 1 further has an interior surface 11 and an exterior surface 13.The top 5 and the sidewall 7 form a cavity 2 for receiving the glasslamp 3. The lamp base 1 further has an inner diameter A and an outerdiameter B. Hollow cylindrical electrical contacts 15 extend from andthrough the bottom 5 of the base 1. The lamp bases are usually formedfrom steel copper, alloy, brass, stainless steel, aluminum, and thelike.

The glass lamp 3 has an open top end 17 and a generally cylindrical sidewall 19, which extends to form a closed lower end, which is not shown.The side wall 19 has an interior surface, not shown, and an exteriorsurface 23. As shown in FIG. 1, a recess 25 extends around thecircumference of the glass lamp 3 below the top end 17 of the lamp. Thepresent invention, however, may also be used with glass lamps withoutsuch recesses. The top end 17 of the glass lamp 3 has a diameter C whichis generally smaller than the inner diameter B of the lamp base 1 suchthat the top end 17 of the glass lamp fits inside or mates with the base1 leaving a small annular space between the interior surface of the baseand the exterior surface of the glass lamp. The glass lamp 3 also hascurrent carrying wires inside the lamp, not shown, which extend throughthe open top end 17 and are threaded through openings 20 of theelectrical contacts 15.

FIGS. 2 and 4 illustrate two embodiments of a foamable coupling of thepresent invention, a ring-shaped coupling 27 and a C-shaped coupling 29,respectively. The ring-shaped coupling 27 has an outer surface 24, aninner surface 26, an outer diameter D, an inner diameter E, a width F,and a thickness G. FIG. 3 is a cross-sectional view of the ring 27 takenalong line 3—3. The foamable coupling may also be a rectangular-shapedstrip, or comprise a plurality of small rectangular-shaped strips.Preferably the foamable coupling is a single piece ring-shaped orC-shaped coupling as shown in FIGS. 2 and 4. It will be appreciated bythose of ordinary skill in the art that the diameter, width, thickness,and shape of the foamable coupling will be directly dependent on thetype and size of glass lamps and bases used in the lamp assembly.

In a preferred method of the present invention for securing the glasslamp 3 in the base 1, a ring-shaped foamable coupling 27 is placed overthe top end 17 of the glass lamp 3 and placed in recess 25 as shown inFIG. 6. The foamable coupling may also be shaped or profiled to fit thecontour of recess of the glass lamp. FIG. 5A is a cross-sectional viewof the C-shaped foamable coupling 29 of FIG. 4 taken along line 5—5. Asshown in FIG. 5A, the C-shaped coupling 29 has a parabolic shape, whichis shaped to fit into the recess 25 of the glass lamp 3 of FIG. 1. Inanother embodiment shown in FIG. 5B, a thin layer of adhesive 22 hasbeen extruded on the inner surface 26 of the C-shaped foamable couplingin order to assist in adhering the foamable coupling 29 in the recess 25of the glass lamp 3. Alternatively, it will be appreciated by those ofordinary skill in the art that a very thin layer of adhesive may beapplied in the recess 25 of the glass lamp to ensure adhesion of thefoamable coupling 29 to the glass lamp. The foamable coupling may alsoinclude additives to make the coupling more elastomeric in nature sothat minimal force is needed to place the ring-shaped coupling over thetop of the glass lamp thereby reducing the risk of breaking the glasslamp during the manufacturing process. If the foamable coupling is arectangular-shaped strip, the coupling is simply wrapped around therecess 25 of the glass lamp. If the foamable coupling comprises aplurality of smaller rectangular-shaped strips, the strips are placedequidistant from one another around the recess 25 of the glass lamp.

As further shown in FIG. 7, after the coupling 27 has been placed aroundthe glass lamp in the recess, the top end 17 of the glass lamp 3 isinserted into the base 1 such that there is a small annular space 30between the ring-shaped foamable coupling 27 and the interior surface 11of the base. Subsequently, the entire lamp assembly is heated to atemperature, which causes the ring-shaped coupling 27 to foam and cure.During the foaming process, the coupling 27 expands radially and thusdoes not expand over the rim 9 of the base 1 or onto the electricalcontacts 15 in the bottom of the base 1. FIG. 8 shows the foamed andcured ring-shaped coupling 31 filling the annular space 30 and securelyaffixing the glass lamp 3 in the base 1.

Another preferred method for securing a glass lamp in a base is shown inFIGS. 9-11. Referring now to FIG. 9, a ring-shaped foamable coupling 27,or other shaped coupling, is placed in intimate contact with theinterior surface 11 of the side wall 7 of the base such that an upperedge 28 of the coupling 27 is only slightly below the rim 9 of the base.The diameter D of the foamable coupling 7 as shown in FIG. 2 is slightlysmaller than the diameter A of the base as shown in FIG. 1 in order forthe foamable coupling to be inserted into the base 1. However, thediameter D of the coupling 27 cannot be too much smaller than thediameter A of the base or the coupling 27 will not stay in place in thebase. One of ordinary skill in the art will appreciate that a smallamount of adhesive may be placed on the interior surface 11 of the sidewall 7 in order to ensure adhesion of the foamable coupling 27 to theinterior surface 11 prior to inserting the glass lamp into the base.Alternatively, adhesive may be extruded onto the outer wall 24 of thefoamable coupling 27 to ensure adhesion of the coupling to the interiorsurface 11 of the side wall.

In order to avoid the use of an additional adhesive and to provide foreasier insertion of the foamable coupling 27 into the base 1, thecoupling may be oriented to have a recoverable diameter. Such anextruded foamable coupling 27 is placed in the base 1 and heated to atemperature which causes the coupling to recover in diameter to fittightly into the base 1, but which does not cause foaming and curing ofthe coupling 27.

After insertion of the foamable coupling 27 in the base 1, the glasslamp 3 is inserted into the base as shown in FIG. 10. Subsequently, theentire light bulb assembly is heated to a temperature, which causes thering-shaped coupling to foam and cure. FIG. 8 again shows the foamed andcured coupling 31 securely affixing the glass lamp 3 in the base 1.

FIG. 11 is a top perspective view of a lamp base 1 with a foamedring-shaped coupling 31 affixed to the interior surface 11 of sidewall7. As shown in FIG. 9, during the foaming process, the coupling 31expands radially and thus the upper edge 28 of the foamed coupling 31does not expand over the rim 9 of the base 1 or onto the electricalcontacts 15 in the bottom of the base 1.

Suitable compositions for the foamable coupling of the present inventionwill be EVA or EMA based copolymer compositions having foamingtemperatures in the range of the intended application and which canwithstand prolonged use at elevated temperatures. In general, thefoamable composition will contain an EVA and/or EMA base copolymer and ablowing agent for foaming the base copolymer. In addition, the foamablecomposition may include antioxidants, chemical crosslinking agents,radiation crosslinking promoters, tackifiers, fillers, flame retardants,and the like.

A single EVA or EMA copolymer, a blend of different EVA copolymers, or ablend of EVA and EMA copolymers may be used to form the base polymer forthe foamable composition. EVA refers to a random copolymer ofpolyethylene with vinyl acetate, while EMA refers to a random copolymerof ethylene and an ester type acrylic derivative. The acrylic derivativemay be based on methyl acrylate (-MA) or ethyl acrylate (-EA) or butylacrylate (-BA). Furthermore one may employ methacrylic acid, instead ofesters of acrylic acids for improved adhesion and/or increased stiffnessin the coupling composition. Along the same lines, one may choose toemploy functionalized derivatives of these copolymers, which performsimilarly to the parent polymer itself. Typical functional groups orterpolymers for enhanced bond strength may be a maleic anhydride or anacrylic acid. Similarly one may use a terpolymer wherein the additionalgroup may be a maleic anhydride or an acrylic acid.

Numerous EVA and EMA based copolymers are commercially available.Preferred EVA copolymers include Escorene® LD-761 manufactured by Exxon,Elvax® 460 manufactured by Dupont, and Evatane® 2805 manufactured by ELFAtochem, Inc. The vinyl acetate concentration of the EVA copolymers ispreferably about 9-33%, more preferably about 18-30%, and mostpreferably about 25-29%. The melt index of the EVA copolymers ispreferably between 0.5 and 150 and more preferably between 1 and 10.Preferred EMA copolymers are Optema® TC 120 manufactured by ExxonMobilChemical Company, Lotryl® EMA Grade 24MA005 manufactured by AtofinaChemicals, and Emac® manufactured by Chevron Chemical Company. Themethyl acrylate content of the EMA copolymer is preferably about 9-33%,more preferably about 16-30% and most preferably about 20-30%. The meltindex of the chosen EMA copolymer is preferably between 0.25 and 45 andmore preferably between 0.5 and 5.

Blowing agents are chosen to effect foaming and expansion of thefoamable composition at an activation temperature from 120° C. and 200°C. Suitable blowing agents will include azodicarbonamide andbenzenesulfonyl hydrazide. Suitable azodicarbonamide blowing agentsinclude Celogen® AZ 130 or 3990, and modified azodicarbonamide agentsinclude Celogen® 754 or 765 all from Uniroyal Chemical. Suitablebezenesulfonyl hydrazide blowing agents includep,p′oxybis(bezenesulfonyl hydrazide), sold as Celogen® OT, andp-toulene-sulfonyl hydrazide, sold as Celogen TSH, both also fromUniroyal Chemical. The blowing agent may also be a combination of agentsdepending on the degree of expansion desired for the particularapplication. Certain fillers, such as zinc oxide (Kadox 911 manufacturedby Marman/Keystone Industries), may also act as activators for theblowing agent and aid in the required expansion. The amount of activatoradded will depend on the choice of blowing agent and the amount ofexpansion required.

Another type of blowing agent particularly useful in the presentinvention is a microencapsulated blowing agent. Such blowing agentsgenerally comprise a spherical polymeric shell and a gas or a liquidblowing agent within the shell. When the polymeric shell is heated, theshell softens and the gas or fluid within the shell increases inpressure causing the shell to expand. When the heat source is removed,the polymeric shell hardens and remains in its expanded state. Theexpansion function of such microencapsulated blowing agents may also beincreased by the addition of one or more of the conventional blowingagents previously discussed.

The polymeric shell generally comprises copolymers of vinyl chloride,vinylidene chloride, acrylonitrile, methacrylonitrile, styrene, andcombinations thereof. Preferably, the polymeric shell encapsulates ahydrocarbon-based gas such as isopentane or isobutane. With respect tothe present invention, the unexpanded polymer shells preferably have asize ranging from about 3 μm to 60 μm, more preferably from about 10 μmto 40 μm, and most preferably from about 15 μm to 30 μm.

Preferred encapsulated blowing agents include Expancel® polymericmicrospheres manufactured by Akzo Nobel. In general, such microsphereshave an unexpanded diameter between 6 μm and 40 μm and an expandeddiameter between 20 μm and 150 μm. More preferably, the encapsulatedblowing agent is Expancel® 091-DU-80, and most preferably Expancel®092-DU-120 both of which have polymeric shells comprising copolymers ofacrylonitrile and methacrylonitrile and encapsulate isopentane gas.

The chemical crosslinking agent is preferably a free radicalcrosslinking agent compatible with the EVA or EMA base polymer.Preferred chemical crosslinking agents are peroxides such asbis(t-butylperoxy)diisopropylbenzene, di-(2-t-butyl peroxyisopropylbenzene) (Vulcup 40KE), 1,1-d-t-butylperoxy-3,3,5-trimethylcyclohexane,4,4-di-t-butylperoxy n-butyl valerate (Trigonox), and dicumyl peroxide(Dicup). A preferred chemical crosslinking agent is with Vulcup 40 KEmanufactured by Hercules Industries Inc.

The blowing agent and the chemical crosslinking agent will be chosen sothat the chemical crosslinking agent has an activation temperatureapproximately the same as the blowing agent. For example, the chemicalcrosslinking agent may have an activation temperature slightly above orbelow that of the blowing agent, so that the foam maintains stabilityduring expansion. Desirably, the activation temperature of the blowingagent will be chosen so that the blowing agent is not easilyaccidentally activated but is only activated when it encounterstemperatures in which it is desired that the foamable composition beactivated.

In a preferred embodiment, a radiation crosslinking promoter is used inaddition to the chemical crosslinking agent. While those of ordinaryskill in the art would normally consider the use of a radiationcrosslinking promoter in addition to a chemical crosslinking agentredundant and unnecessary, the addition of a radiation crosslinkingpromoter yielded surprising results. Foamable compositions of thepresent invention incorporating both a chemical crosslinking agent and aradiation crosslinking promoter exhibited increased stability of thefoamed compositions at high temperatures. The radiation crosslinkingpromoter may be chosen from among those conventionally used to promotecrosslinking of polymers, including triallyl cynurate (TAC), triallylisocyanurate (TAIC), triallyl trimellitate, triallyl trimesate,tetrallyl pyromellitate, the dually ester of1,1,3,-trimethyl-5-carboxy-3-(4-carboxyphenyl)indene, trimethylolpropanetrimellitate (TMPTM), pentaerythritol trimethacrylate,tri(2-acryloxyethyl)isocyanurate, tri(2-methacryloxyethyl)trimellitate,and the like and combinations thereof. A preferred radiationcrosslinking promoter is TMPTM commercially available as Sartomer SR 350from Sartomer Company.

The tackifier will be chosen to enhance the tackiness of the foamablecompositions on activation but not such that the composition willexhibit tackiness prior to or after activation, or after cooling andsolidification. Desirably, the tackifier will have a relatively lowmolecular weight, no significant crystallinity, a ring and ballsoftening point above at least 50° C. and will be compatible with theEVA or EMA base polymer. Suitable tackifiers include novolak resins,partially polymerized rosins, tall oil rosin esters, low molecularweight aromatic thermoplastic resins, Picco® and Piccotac® resins fromHercules Chemical Company. A preferred tackifier is Piccotac® 95. Inaddition, some functionalized aliphatic polyamide hot melt resins madeby Henkel Adhesives or Arizona Chemicals may also be used to improve thehot tack properties of the coupling and ultimately the bond strengthbetween the glass lamp and metal base. A preferred polyamide hot meltresin is Macromelt® 6239 from Henkel Adhesives and is preferably addedto the foamable composition in an amount of 5 to 50% by weight, and morepreferably 10 to 15% by weight.

Suitable fillers for the composition include, zinc oxide, barium sulfate(Huberite), calcium carbonate, magnesium hydroxide, carbon black, andthe like. A preferred carbon black is Raven C Ultra Beads manufacturedby Columbian Chemicals Company. Ferromagnetic particles, including ironpowder, nickel flakes and the like, may also be added for inductiveheating, foaming and curing of the composition.

Flame retardants may also be added in an amount as will provide flameretardancy for the foamable ring. Suitable flame retardants includepolybrominated aromatics, such as decabromobiphenyl, and the like incombination with inorganic materials such as antimony trioxide.Antioxidants, foaming agents, adhesion promoters, UV screeners,plasticizers, pigments and the like may also be employed in conventionalamounts.

Exemplary formulations for the foamable composition using a conventionalazodicabonamide and benzenesulfonyl hydrazide blowing agents are listedbelow in Table I with A1 being preferred, A2 being more preferred, andA3 being the most preferred formulation.

TABLE I Formulations By Weight Percent Ingredient A1 A2 A3 EVA/EMACopolymer 50-80 60-80 78.5^(a) Tackifier  0-30  3-15 5^(b) Antioxidant0.25-5   0.5-4   3^(c) Chemical Crosslinking Agent 0.5-5   1-4 3^(d)Blowing Agent  1-10 2-7 3^(e) Blowing Agent Activator  0-10 1-7  2.5^(f)Radiation Crosslinking Promoter 0.5-5   1-4  2.5^(g) Fillers  0-30  0-20 2.5^(h) ^(a)ATEVA 2803 ^(b)Piccotac ® 95 ^(c)2% Irganox 1010, 1% Cyanox1212 ^(d)Vulcup 40KE ^(e)Celogen ® OT-72DG ^(f)Kadox 911 ^(g)Sartomer SR350 ^(h)Carbon Black Raven C Ultra Beads

In order to achieve optimal performance of the blowing agents and therequired level of foaming and curing, the foamable compositions in TableI should be heated to a temperature from 130 to 200° C., more preferably150 to 180° C., and most preferably to 165° C.

Exemplary formulations for the foamable composition using amicroencapsulated blowing agent are listed below in Table II with B1being preferred, B2 being more preferred, and B3 being the mostpreferred formulation.

TABLE II Formulation By Weight Percent Ingredient B1 B2 B3 EVA/EMACopolymer 50-80 60-80 74^(a) Tackifier  0-30  3-15 5^(b) Antioxidant0.25-5   0.5-4   3^(c) Microencapsulated Blowing  1-10 1-7 5^(d) AgentChemical Crosslinking Agent 0.5-5   1-4 3^(e) Chemical Blowing Agent 0-50-3 0 Blowing Agent Activator  0-10 0-6 4^(f) Radiation CrosslinkingPromoter 0.5-5   1-4 2.5^(g) Fillers  0-30  0-20 2.5^(h) ^(a)Escorene ®LD 761 ^(b)Piccotac ® 95 ^(c)2% Irganox 1010, 1% Cyanox 1212^(d)Expancel ® 092-DU-120 ^(e)Vulcup 40KE ^(f)Kadox 911 ^(g)Sartomer SR350 ^(h)Carbon Black Raven C Ultra Beads

In order to achieve optimal performance of the blowing agents and therequired level of foaming and curing, the foamable compositions in TableII should be heated to a temperature from 130 to 200° C., morepreferably 150 to 190° C., and most preferably to 160° C.

The foamable compositions of the present invention may be prepared byknown conventional methods in the art of polymer blending, such asmixing in a high shear Banbury or Brabender type mixer. In a commonlyused method involving high shear compounding of peroxide ladenformulations, the compositions are formed in Banbury mixer using a oneor two pass (batch) process, with the one pass process being preferred.

In the two pass process, the Banbury mixer is generally not heated, themotor is placed in high gear for high rotation speeds and the ram is setat about 100 psi. Initially, all of the ingredients except the peroxideand the blowing agent(s) are mixed in the Banbury. In particular, duringthe first pass, all of the ingredients except the tackifier andradiation crosslinking promoter are blended in the Banbury forapproximately 1.0-1.5 minutes with the ram in the down position. Thetackifier and radiation crosslinking promoter are subsequently added,and the batch is thoroughly blended for 1.5-3.0 minutes with the ram inthe neutral position. The batch is further blended for an addition0.5-1.0 minutes with the ram in the up position. The temperature of theresulting “first pass” batch as its exits the Banbury is approximately120 to 130° C. The “first pass” batch is then processed through apelletizing extruder operating at low rpm with barrel temperaturesettings of about 80-90° C., with the pelletizing die temperature beingapproximately 90-110° C.

During the “second pass,” the “first pass” pellets and the peroxide andblowing agent(s) are placed in the unheated Banbury having operatingconditions as set forth above. The “second pass” batch is blended for0.8-0.9 minutes with the ram in the down position and then for 0.2-1.1minutes with the ram in the neutral position. Special attention must bepaid to the overall operating conditions during the “second pass” toensure that temperature of the batch does not reach or exceed theactivation temperature of the peroxide and blowing agent(s). For themost preferred compositions described above, the temperature of thecomposition during the “second pass” preferably does not exceed about110° C., and more preferably does not exceed 105° C. The temperature ofthe resulting “second pass” batch as it exits the Banbury is mostpreferably approximately 95-105° C. The “second pass” batch is thenprocessed through a pelletizing extruder at the same operatingconditions set forth above producing the final composition pellets.

In the preferred one batch process using a Model F-80 Banbury mixer, thepolymers, carbon black, and any other fillers are first added to theBanbury mixer with the rotors set at 60 rpm and are mixed to a flux forabout 1.5 minutes. Low viscosity materials including the tackifier andother liquid ingredients are then added into the existing mixture andmixed for another 2.0 minutes with the rotor speed dropped to 25 rpm.Finally, the thermally sensitive materials such as the blowing agent andthe crosslinking agent are added into the composition and mixed foranother 1.5 minutes before being extruded into the final compositionpellets. The temperature of the foamable composition as it passes intothe extruder is about 100° C. with the extruder operating at the sameconditions set forth above. Those of ordinary skill in the art ofcompounding heat sensitive materials will recognize the need to adjustmachine parameters to the needs of the formulation, depending upon themelting point and viscosity of the base resin, filler content and theactivation temperature of the peroxide and the blowing agents used.

The final composition pellets may then be extruded, compression molded,or injection molded into foamable couplings for use in securing glasslamps to bases. Preferably, the final composition pellets are processedthrough an extruder. During the extrusion process, care must be taken toavoid generating too much shear heat in the extruder barrel and tomaintain the exit melt temperature of the composition well under theactivation temperatures of both the blowing agent(s) and the peroxide.In particular, the temperature of the composition during the extrusionprocess should not exceed about 105° C.

The final composition pellets may be extruded into ring-shaped,C-shaped, or rectangular-shaped foamable couplings, which are ready tobe used in a lamp assembly as previously discussed. Alternatively, thefinal composition pellets may be extruded into sheets, and ring-shaped,C-shaped or rectangular-shaped foamable couplings may be cut out of thesheets. Preferably, the final composition pellets are extruded intoring-shaped or C-shaped foamable couplings. After they have beenextruded, the couplings may be physically crosslinked with gammaradiation or a high energy electron beam to improve heat resistance.

Upon testing of the foamable compositions in Table I and Table II, itwas found that the use of higher concentrations of Expancel® 092-DU-120without a traditional blowing agent had dramatic and unexpected results.The shelf life of the unfoamed composition was much longer thanexpected, as indicated by comparative expansion characteristics ofmaterials stored at 45° C. and 80% relative humidity. In addition, therigidity of the foamed composition, was surprisingly much higher thanexpected, when compared against foams obtained with traditional chemicalblowing agents as indicated by secant modulii values of the two foamedcompositions at equivalent voids content. The use of thismicroencapsulated blowing agent composition also resulted in a largeincrease in the torque required to dislodge the base from the glass. Theuse of Expancel® 092-DU-120 further assisted in maintaining theintegrity of the cell structure of the composition after foaming whensubjected to elevated temperatures (140° C.) for a substantial period oftime (3500 hours).

Accelerated Aging Tests

Test samples of compositions B2 and B3 set forth in Tables III and IVbelow were prepared according to the two batch process described above.

TABLE III Formula B2 (based on Formula B2 from TABLE II) IngredientsWeight Percent (% W/W) ATEVA 2803  74.00% Piccotac ® 95  5.00% Vulcup 40KE  3.00% Celogen ® OT-72DG  5.00% Kadox 911  4.00% Irganox 1010  2.00%Cyanox 1212  1.00% Sartomer SR 350  2.50% Raven C Ultra Beads  2.50%Expancel ® 91-DU  1.00% Total 100.00%

TABLE IV Formula B3 (from TABLE II) Ingredients Weight Percent (% W/W)Evatane ® 28-05  74.00% Piccotac ® 95  5.00% Vulcup 40 KE  3.00% Kadox911  4.00% Irganox 1010  2.00% Cyanox 1212  1.00% Sartomer SR 350  2.50%Raven C Ultra Beads  2.50% Expancel ® 092-DU-12-  6.00% Total 100.00%

The final B2 and B3 composition pellets were separately placed into a6×6×0.040 inch mold sandwiched between two Teflon sheets and steel backplates. This mold assembly was then placed in the platens of a hydraulichot press heated to 100° C. The mold assembly was preheated toapproximately 60 seconds under a load of 1000 psi. The pressure on themold assembly was then increased to 30,000 psi then released to zero psithree times. This allowed any air in the mold assembly to be expelled.The pressure was then increased to 30,000 psi for 2 minutes. Thepressure on the mold assembly was then released, and the mold was placedinto a cold press where the pressure was increased to 30,000 psi andheld for 1 minute in order to cool the mold assembly. The pressure onthe mold assembly was released, and the mold was released from theassembly. The 6×6×0.040 inch molded plaque of material was removed fromthe mold and any excess flashing was trimmed from the plaque.

Test strips 0.25 inches in width, 0.40 inches thick and 6 inches longwere die cut from the molded plaques. The test strips were place onTeflon coated cookie sheets and aged in air circulating ovens preheatedto 140° C. and 160° C. Periodically specimens of both materials wereremoved from the oven for elongation testing. Specimens were allowed tocool to room temperature prior to testing. All testing was carried outon an INSTRON® tensile testing machine at a crosshead speed of 50mm/min. Results of the elongation testing are shown in Tables V and VIbelow.

TABLE V Sample Elongation Formula B2 Expanded 160° C. for 15 Minutes 1400% 2 300% 3 420% Average 413% Expanded Aged for 2600 hrs. @ 140° C. 1240% 2 210% 3 200% Average 217% Expanded Aged for 3500 hrs. @ 140° C. 180% 2 30% 3 50% Average 53%

TABLE VI Sample Elongation Formula B3 Expanded 160° C. for 15 Minutes 1100% 2 140% 3 120% Average 120% Expanded Aged for 2600 hrs. @ 140° C. 1220% 2 210% 3 210% Average 213% Expanded Aged for 3500 hrs. @ 140° C. 1120% 2 140% 3 120% Average 127%

As shown in the Tables V and VI, both B2 and B3 have sufficientelongation retention after 2600 hours of aging at 140° C. to withstandthe IEC requirements for lamp assemblies of 2000 hours at 140° C.However, the superior improved thermal aging stability of the B3 teststrips aged at 140° C. for 3500 hours was unexpected.

Bonding Performance Tests

The bonding performance of formulations A3 from Table 1, and B2 and B3from Tables III and IV were also tested. The formulations were made bythe two-batch process set forth above. The final pellets for eachformulation were then extruded into a tubular shape having a wallthickness of 0.036 inches. Subsequently, ring-shaped couplings having acut length (height) of 0.1000±0.010 inches were cut from the extrudedtubing. The ring-shaped couplings were then each placed in the metalbase of a size T12 fluorescent lamp assembly provided by Osram/Sylvania.The metal bases were then placed onto the glass lamp of the T12 lampassembly. These resulting assemblies were placed into a forced air ovenat the temperatures and for the times listed below in Table VII in orderto securely affix the glass lamp into the metal lamp base. The sampleswere then removed from the oven and cooled for at least 20 minutesbefore any testing was done. The lamp assemblies were then placed one ata time in a torque-testing fixture with a force gauge, and the torque(inch/lb) required to rotate the metal lamp base more than 3° or breakthe metal base completely free from the glass lamp was measured. Theresults of these torque tests are set forth in Table VII.

TABLE VII Formula Temperature (° C.) Time (sec.) Torque (in/lbs) A3 20090 4 B2 200 90 26 B3 200 90 31 B2 200 120 9 B3 200 120 14 B2 325 60 10B2 325 60 12 B3 325 60 15 B3 325 60 20

As shown in Table VII, the B3 couplings had better bonding strength thanB2 couplings, which again was unexpected.

Shelf Life Tests

Tests were also performed on B2 and B3 compositions to determine theshelf life of the compositions or the amount of time the compositionscan be stored before comprising performance of the compositions. Thesamples used in the shelf life tests were prepared using an 8×8×0.040inch compression mold with nine 1-inch diameter holes cut out of themold. The mold was placed on a Teflon® sheet backed by a steel plate. Ameasured amount of the compositions was distributed within the 1-inchdiameter holes of the mold and another Teflon® sheet with a steel backplate was placed on top of the mold to complete the mold assembly. Themold assembly was then subjected to the same process set forth withrespect to the Accelerated Aging Tests. The 1-inch round compressionmolded disks formed from B2 and B3 were each divided into two groups.The first group was labeled as a “Control” and was placed intoindividual zip lock bags. The zip lock bags were stored at roomtemperature, approximately 19° C. The second group of disks was labeledas “Shelf Life Study” and was placed into a humidity chamber set to atemperature of 45° C. with a relative humidity setting of 80%.

The unexpanded B2 and B3 “Shelf Life Study” disks were removed from thehumidity chamber after exposure to the hot and humid environment forthree, six, and twelve weeks. Each time the B2 and B3 Shelf Life Diskswere removed from the humidity chamber, they were compared to theunexpanded “Control” disks. Subsequently both the B2 and B3 “Shelf LifeStudy” and “Control” disks were placed into a baking pan containingcompacted PTFE powder. The pan was then placed in an air-circulatingoven pre-heated to a temperature of 180° C. for 20 minutes allowing thedisks to fully expand. After the expansion process, the “Control” disksand the “Shelf Life Study” disks were removed from the oven and allowedto cool at room temperature. The expanded “Control” disks were thencarefully compared to the expanded “Shelf Life Study” disks.

FIG. 12 is photograph of three disks, 12A, 12B, and 12C used in thestudy made in accordance with formula B2. Disk 12A is an unexpanded“Control” disk. Disk 12B is a “Control” disk that was stored at roomtemperature for 6 weeks and then foamed and cured as set forth above.Disk 12C was subjected to 80% relative humidity at 45° C. for six weeksand then foamed and cured as set forth above. Similarly, FIG. 13 is aphotograph of three disks, 13A, 13B, and 13C used in the study made inaccordance with formula B3. Again, disk 13A is an unexpanded “Control”disk. Disk 13B is a “Control” disk that was stored at room temperaturefor 6 weeks and then foamed and cured. Disk 13C was subjected to 80%relative humidity at 45° C. for six weeks and then foamed and cured asset forth above.

As can be seen in FIG. 12, disk 12C that was subjected to the heat andhumidity for six weeks failed to expand much in the radially direction.In contrast, as shown in FIG. 13, disk 13C was well foamed and evenlyformed after being subjected to heat and humidity. Again, the B3 disk'sincreased resistance to heat and humidity was unexpected.

Secant Modulus Testing

Finally, the secant modulus of formulas B2 and B3 were tested. Samplestrips ofB2 and B3 foamable material were made in accordance withprocess set forth with respect to the Accelerated Aging Testing. Thesecant modulus was then tested according to ASTM standards using anINSTRON® tensile testing apparatus for unexpanded sample strips andsample strips that had been expanded for 120 seconds at 200° C. The jawsof the INSTRON® tensile testing apparatus were set at 100 mm apart. Thesecant modulus data is set forth below in Table VIII.

TABLE VIII 2% Secant Modulus (psi) Expanded for Formula Unexpanded 120Seconds at 200° C. B2 1709 195 B3 1980 1601

The increased stability of the secant modulus for the B3 formula wasunexpected.

While the present invention with its several embodiments has beendescribed in detail, it should be understood that various modificationsmay be made to the present invention without departing from the scope ofthe invention. The following claims, including all equivalents definethe scope of the invention.

What is claimed is:
 1. A lamp assembly comprising: a base having a topand side walls forming a cavity with an interior surface; a glass lamphaving at least one end with an exterior surface inserted in the basecavity; and a foamable coupling positioned between the interior surfaceof the base and the exterior surface of the glass lamp, said couplingcomprising a copolymer selected from the group consisting of ethylenevinyl acetate, ethylene methyl acrylate, ethylene butyl acrylate,ethylene ethyl acrylate, ethylene methacrylic acid, and mixturesthereof, a blowing agent, a chemical crosslinking agent and a radiationcrosslinking promoter; wherein when the base and glass lamp are heated,the foamable coupling expands and securely affixes the glass lamp in thebase.
 2. The lamp assembly of claim 1 wherein the coupling furthercomprises at least one tackifier, antioxidant, filler or a combinationthereof.
 3. The lamp assembly of claim 2 wherein the coupling comprises:from about 60 to 80 percent by weight of at least one copolymer whereinthe copolymer is selected from the group consisting of ethylene vinylacetate, ethylene methyl acrylate, ethylene butyl acrylate, ethyleneethyl acrylate, ethylene methacrylic acid, and mixtures thereof; fromabout 2 to 7 percent by weight of at least one chemical blowing agent;from about 3 to 15 percent by weight of at least one tackifier; fromabout 1 to 7 percent by weight of at least one peroxide; from about 0.5to 5 percent by weight of at least one antioxidant; from about 1 to 4percent by weight of at least one radiation crosslinking promoter; andfrom about 0 to 20 percent by weight of at least one filler.
 4. The lampassembly of claim 1 wherein the base and the glass lamp are heated to atemperature from 130-200° C.
 5. The lamp assembly of claim 1 wherein thebase and glass lamp are heated to a temperature from 150-180° C.
 6. Thelamp assembly of claim 1 wherein the base and glass lamp are heated to atemperature of 165° C.
 7. The lamp assembly of claim 1 wherein theblowing agent is a microencapsulated blowing agent present in an amountfrom 1 to 10 percent by weight.
 8. The lamp assembly of claim 7 whereinthe base and glass lamp are heated to a temperature from 130-200° C. 9.The lamp assembly of claim 7 wherein the base is heated to a temperatureof from about 150-190° C.
 10. The lamp assembly of claim 7 wherein thebase is heated to a temperature of 160° C.
 11. The lamp assembly ofclaim 1 wherein the foamable coupling is ring-shaped, C-shaped,square-shaped, or rectangular-shaped.
 12. The lamp assembly of claim 1wherein when the base and glass lamp are heated the foamable couplingexpands primarily in the radial direction.
 13. A lamp assemblycomprising: a base having a top and side walls forming a cavity with aninterior surface; a glass lamp having at least one end with an exteriorsurface inserted in the base cavity; and a foamable coupling positionedbetween the interior surface of the base and the exterior surface of theglass lamp, said coupling comprising a non-pressure sensitive foamablecomposition comprising from about 50 to 80 percent by weight of at leastone copolymer selected from the group consisting of ethylene vinylacetate, ethylene methyl acrylate, ethylene butyl acrylate, ethyleneethyl acrylate, ethylene methacrylic acid, and mixtures thereof; fromabout 1 to 10 percent by weight of a microencapsulated blowing agent;from about 0 to 30 percent by weight of at least one tackifier; fromabout 0.5 to 5 percent by weight of at least one peroxide; from about 0to 5 percent by weight of at least one chemical blowing agent; fromabout 1 to 10 percent by weight of a blowing agent activator; from about0.25 to 5 percent by weight of at least one antioxidant; from about 0.5to 5 percent by weight of at least one radiation crosslinking promoter;and from about 0 to 30 percent by weight of at least one filler whereinwhen the base and glass lamp are heated, the foamable coupling expandsand securely affixes the glass lamp in the base.
 14. A coupling forsecurely affixing one end of a light emitting glass lamp in a base, saidcoupling comprising a nonpressure sensitive adhesive foamablecomposition comprising: from about 50 to 80 percent by weight of atleast one copolymer wherein the copolymer is selected from the groupconsisting of ethylene vinyl acetate, ethylene methyl acrylate, ethylenebutyl acrylate, ethylene ethyl acrylate, ethylene methacrylic acid, andmixtures thereof; from about 1 to 10 percent by weight of amicroencapsulated blowing agent; from about 0 to 30 percent by weight ofat least one tackifier; from about 0.5 to 5 percent by weight of atleast one peroxide; from about 0 to 5 percent by weight of at least onechemical blowing agent; from about 1 to 10 percent by weight of ablowing agent activator; from about 0.25 to 5 percent by weight of atleast one antioxidant; from about 0.5 to 5 percent by weight of at leastone radiation crosslinking promoter; and from about 0 to 30 percent byweight of at least one filler.